Calibrating data transmission line spacing on a frame-scanning display device for optically transmitting data to a portable programmable device

ABSTRACT

The invention includes systems and methods for calibrating bit transmission rates in a computer system which uses selected raster lines of a frame-scanning display device for serial data transmission to an external receiving device. A system in accordance with the invention includes a data processor and a frame-scanning display device having a total number of available raster lines per display frame. The computer also has an internal timer which is set to generate timing signals at a predetermined frequency. The data processor is programmed to count the number of timing signals and the number of frame scans of the frame-scanning display device which occur during a selected measurement period. The selected measurement period is preferably defined by the occurrence of a predetermined number of frame scans. The data processor is further programmed to calculate a frame scan period of the frame-scanning display device based upon the predetermined frequency of the timing signals, the predetermined number of timing signals, and the number of frame scans counted while counting the predetermined number of timing signals. The frame scan frequency is used to determine the correct spacing of the data transmission raster lines relative to each other within the total number of available raster lines. This spacing establishes a desired serial transmission bit rate to the external receiving device.

TECHNICAL FIELD

This invention relates to systems and methods for transmitting datausing selected raster lines of a frame-scanning display device such as aCRT (cathode ray tube).

BACKGROUND OF THE INVENTION

In recent years, there has been an increasing use of compact,pocket-size electronic personal organizers that store personalscheduling information such as appointments, tasks, phone numbers,flight schedules, alarms, birthdays, and anniversaries. Some of the morecommon electronic organizers are akin to handheld calculators. They havea full input keyboard with both numeric keys and alphabet keys, as wellas special function keys. The organizers also have a liquid crystaldisplay (LCD) which often displays full sentences and rudimentarygraphics.

Pocket-size personal organizers prove most useful to busy individualswho are frequently traveling or always on the move from one meeting tothe next appointment. Unfortunately, due to their hectic schedules,these individuals are the people most likely to forget their personalorganizers during the frantic rush to gather documents, files, laptops,cellular phones, and travel tickets before heading off to the airport ortrain depot. It would be desirable to reduce the number of electronicdevices that these individuals need to remember for each outing.

Electronic watches have evolved to the point that they can function aspersonal organizers. Like the pocket-size devices described above, suchwatches can be programmed with certain key appointments, tasks, phonenumbers, flight schedules, alarms, birthdays, and anniversaries. Sincewatches are part of everyday fashion attire, they are more convenient tocarry and less likely to be forgotten by busy people. However, it ismuch more difficult to enter data into a watch than it is to enter thesame data into a pocket-size personal organizer. This difficulty is duein large part to the limited number of input buttons and displaycharacters available on reasonably-sized watches. Most watches arelimited to having only three or four input buttons. A wearer programs awatch by depressing one or more buttons several times to cycle throughvarious menu options. Once an option is selected, the user depressesanother button or buttons to input the desired information. These inputtechniques are inconvenient and difficult to remember. Such techniquesare particularly inconvenient when a wearer wishes to enter an entiremonth's schedule. Although watches have been made with larger numbers ofinput keys, such watches are usually much too large for comfort, andtend to be particularly unattractive.

Apart from personal organizers, it is common for many people to maintainappointment calendars and task lists on their personal computers. Oneexample time management software is Microsoft's® Schedule™ for Windows®which maintains daily appointment schedules, to-do lists, personalnotes, and calendar planning. This information is often a duplicate ofthat maintained on the portable personal organizer.

Timex Corporation of Middlebury, Conn., has recently introduced theTimex® Data-Link™ watch. This watch utilizes new technology fortransferring information from a personal computer to a watch. Thissystem is more fully disclosed and described in U.S. patent applicationSer. No. 08/155,326 filed Oct. 22, 1993, now U.S. Pat. No. 5,488,571, inthe names of Jacobs and Insero, and assigned to Timex Corporation. Thewatch case has an optical sensor which is connected to a digital serialreceiver, better known as a UART (universal asynchronousreceiver/transmitter), which is incorporated into an integrated circuitcontrolling the time keeping functions of the watch. The watch's opticalsensor and UART expect to receive a serial bit transmission in the formof light pulses at a fixed bit rate. A pulse represents a binary `0`bit, and the absence of a pulse represents a binary `1` bit.

The CRT (cathode ray tube) or other scanned-pixel display of a personalcomputer is used to provide light pulses to the watch. Although itappears to a human viewer that all pixels of a CRT are illuminatedsimultaneously, the pixels are actually illuminated individually, one ata time, by an electron beam which sequentially scans each row or rasterline of pixels beginning with the top raster line and ending with thebottom raster line. It is this characteristic of a CRT and of otherframe-scanning display devices which is utilized to transmit serial datato the Data-Link™ watch.

To transtar data to the watch, the watch is held near and facing theCRT. The computer is programmed to display a sequence of display framesin which spaced data transmission raster lines represent individual bitsof data. Lines are illuminated or not illuminated, depending on whetherthey represent binary `0` bits or binary `1` bits. Each line appears asa continuous pulse of a finite duration to the receiving watch. Thewatch recognizes an illuminated line as a binary `0` bit. It recognizesa non-illuminated line as a binary `1` bit. Generally, ten bits aretransmitted in a single CRT display frame: eight data bits, a start bit,and a stop bit. As used herein, the term "display frame" means a singlescreen-size image made up of a matrix of pixels which form a pluralityof raster lines. A display frame is generally created by sequentiallyilluminating or refreshing the raster lines of the display device.

The UART of the Data-Link™ watch expects to receive data at a veryspecific bit rate of 2048 bits per second. This can be accomplished bycorrectly establishing the spacing of data transmission raster linesused on the display device for data transmission. More specifically, thespacing can be controlled by varying the number of unused raster linesbetween the data transmission raster lines which are selected tocommunicate data bits to the watch. The correct spacing, however,depends on the rate at which the display device scans or updates itspixels and raster lines. Not all display devices use the same scanningrate.

Initial development of the Data-Link™ watch was carried out on displaydevices operating at a screen refresh rate of 60 Hz (all pixelsrefreshed 60 times per second). A mammal calibration routine wasdeveloped for those users with "non-standard" display devices operatingat different refresh rates. The manual calibration routine consistedessentially of repetitively transmitting a test character to the watchand manually increasing or decreasing the bit rate (corresponding to arespectively decreasing or increasing data transmission raster linespacing). This system is disclosed in U.S. patent application Ser. No.08/251224 filed May 31, 1994, in the names of Brzezinski and Dvorachekand assigned to Timex Corporation. Two factors, however, combined tomake this approach less useful. First, it was found that there a numberof "non-standard" display devices in use, requiring some users tomanually calibrate their systems. Second, it was found that the manualcalibration routine was difficult to use. Errors would occur duringcalibration and users had difficulty identifying the sources of thoseerrors. Many times, users had simply not yet learned where to hold thewatch relative to the display device for optimum data reception. Thisled to confusion and an inability for many users to successfullycalibrate their systems.

SUMMARY OF THE INVENTION

The invention described herein was developed in an effort to eliminatethe need for manual calibration of data transfer systems as describedabove. Instead, the computer which is to transmit data is programmed toautomatically determine the frame scan rate or period of the connecteddisplay device. This is accomplished by setting an internal timer of thecomputer to generate timing signals at a predetermined frequency and tocount the number of those timing signals and the number of frame scanswhich occur during a selected measurement period, preferably defined bythe occurrence of a predetermined number of frame scans. The computermonitors the vertical retrace register associated with the displaydevice to determine the number of frame scans which occur during themeasurement period. The time scan period is derived or calculated basedupon the number and predetermined frequency of the timing signals andthe counted numbers of frame scans. Once the frame scan period is known,raster lines which are used to transmit data can be correctly spacedrelative to the total number of available raster lines to set thedesired serial transmission rate to the external receiving device.

BRIEF DESCRIPTION OF THE DRAWINGS

The same reference numerals are used throughout the disclosure toreference like components and features.

FIG. 1 is a diagrammatic illustration of a system for seriallytransferring data to a programmable watch from a desk-top computeraccording to a preferred embodiment of this invention.

FIG. 2 is a block diagram of a computer which forms part of the systemof FIG. 1.

FIG. 3 is diagrammatic front view of a CRT monitor depicting a displayframe having contiguously-scanned lines used to convey bits ofinformation to the programmable watch.

FIG. 4 is a diagrammatic front view of the programmable watch of FIG. 1.

FIG. 5 is a block diagram of an electronic configuration of theprogrammable watch of FIG. 1.

FIG. 6 is a flow diagram of a method comprising preferred steps forcalibrating data transmission lines on a frame-scanning display devicein accordance with the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows a personal electronic time management system 10 accordingto one embodiment of this invention. Time management system 10 includesa computer or computer system 11 and a portable or external informationreceiving device in the form of programmable watch 12. An optical datatransmission interface is provided to enable computer system 11 toprogram watch 12 by transferring programming information thereto.

Watch 12 has an optical sensor 13. Computer system 11 remotely programswatch 12 by optically transmitting a serial stream of data that can bedetected and deciphered by watch 12. The preferred embodiment of thisinvention involves a programmable watch, such as the commerciallyavailable Timex® Data-Link™ watch, which can be configured to functionas a portable personal time manager. Accordingly, the invention isdescribed herein within the context of a programmable watch. However,other forms of external devices can be used, such as pagers and personaldigital assistants (PDAs). As used herein, "portable information device"means a small, portable, electronic apparatus that has limited powerresources and limited rewritable memory capacity. The Data-Link™ watch,for example, is presently constructed with a rewritable memory capacityof approximately 1 Kbyte.

Computer 11 includes a frame or raster scanning graphics display device14, a central processing unit (CPU) 15 having a data processor, memory,and I/O components, and a keyboard 16 (or other input device). Thesecomponents and other internal components of CPU 15 are shown in FIG. 2.As shown, CPU 15 includes a data processor 17 and associated memory 18.CPU 15 also includes non-volatile storage 19 such as a hard disk,general I/O circuits 20 for interfacing with keyboard 16, printers (notshown) and other devices, and a graphics controller 21 which interfacesCPU 15 with display device 14. CPU 15 further includes an internalgeneral purpose timer 24 which can be used to generate periodicinterrupts or for other purposes by application software running on CPU15. Such a timer is found in most types of desktop or personalcomputers. The illustrated computer system is an IBM®-compatible system,although other architectures, such as Apple®-compatible systems, can beemployed. In IBM®-compatible systems, the internal timer is referred toas an 8253 timer. The 8253 timer actually incorporates three timercircuits. Two are used by the computer's internal operating system,while a third is available for application programs. In accordance withthe preferred embodiment of the invention, the third timer of the 8253timer is set to generate timing signals at a predetermined frequency of1000 cycles per second. These timing signals are monitored and countedby data processor 17 as described below.

Visual display device 14 is preferably a CRT (Cathode Ray Tube) monitorsuch as commonly used in personal computers. Other types offrame-scanning and raster-scanning visual display devices, which emithigh-speed light transmissions, could also be used. The graphics displaydevice displays sequential display frames containing graphical images onits monitor screen 22. A "display frame" or "frame" means a single,two-dimensional, screen-size image made up of a matrix of pixels. Thepixels form a plurality of available raster lines for each displayframe. The frames are normally displayed successively at an effectiverate so that they appear visually static or constant on the monitorscreen 22, rather than flickering. In a CRT monitor which operates at 60Hz, all pixels of the monitor screen 22 are refreshed once every 1/60 or0.01667 second. In contrast, the human eye only begins to perceive anon-constant flickering at a much slower frequency of about 10 Hz.

The individual pixels and raster lines of a CRT are illuminatedindividually by an electron beam (i.e., the cathode ray) whichsequentially scans each raster line beginning with the top raster lineand ending with the bottom raster line. The beam is deflectedhorizontally (in the line direction) and vertically (in the fielddirection) to scan an area of the screen to produce a single displayframe. The electron beam strikes phosphors positioned at the screen ofthe CRT monitor to cause them to glow. The phosphors are arrangedaccording to a desired pixel pattern, which is customarily a matrix ofrows and columns. Conventional color VGA monitors typically have aresolution of 640×480 pixels or better. The process of scanning allraster lines a single time and returning the electron beam from thebottom to the top of the display is referred to as a "frame scan." Thetime required to accomplish a single frame scan is referred to as the"frame scan period." The frequency at which frame scans occur (theinverse of the frame scan period), is referred to as the "frame scanfrequency" or "frame scan rate."

As in most modern personal computer systems, the displayed matrix ofdisplay frame pixels is specified by a corresponding matrix of datavalues stored within the memory 18 of CPU 15. The specific area ofmemory 18 designated for storing pixel information is referred to as aframe buffer, and is referenced in FIG. 2 by the numeral 23. Framebuffer 23 is associated with the frame-scanning graphics display device,having individual pixel storage locations corresponding respectively toindividual display frame pixels. Graphics controller 21 reads pixelinformation from frame buffer 23 during each CRT scan to determine thecolor and intensity of each display frame pixel. Data processor 17writes to frame buffer 23 to display desired or specified patterns onCRT 14.

The linear scanning electron beam of CRT 14 is utilized to transmitserial data to programmable watch 12. Specifically, computer 11 usesselected, spaced raster lines of CRT 14 for serial bit transmission towatch 12. Application software loaded in CPU 15 generates a sequence ofdisplay frames having changing patterns of raster lines that aredisplayed on CRT 14. The lines appear at optical sensor 13 as serialdata. Watch 12, through optical sensor 13, monitors the illumination ofthe raster lines of the sequential display frames to reconstruct thetransmitted data.

FIG. 3 shows a specific pattern of selected and spaced raster lines usedto transmit data to watch 12. Assuming that each frame transmits asingle 8-bit byte with start and stop bits, ten raster lines30(1)-30(10) (out of a much larger total number of available rasterlines) are selected for transmitting data. These raster lines will bereferred to herein as "data transmission raster lines," as opposed toother, intervening raster lines which will be referred to as "unusedraster lines." Solid lines in FIG. 3 represent data transmission rasterlines which are illuminated. Dashed raster lines in FIG. 3 representdata transmission raster lines which are not illuminated. Each datatransmission raster line position conveys one data bit of information.Bits having a first binary value, such as a value `0`, are representedby illuminated data transmission lines (e.g., lines 30(1), 30(2), 30(4),and 30(7)30(9)) and bits having, a second binary value, such as a value`1`, are represented by non-illuminated data transmission lines (asillustrated pictorially by the dashed lines 30(3), 30(5), 30(6), and30(10)). The data transmission raster lines are spaced at selectedintervals, with intervening unused or non-selected raster lines, toproduce a desired temporal spacing appropriate for the data receivingelectronics of watch 12.

For each programming instruction or data to be transmitted to the watch,the software resident in the CPU 15 causes the CRT monitor 14 toselectively illuminate the appropriate data transmission raster linesrepresenting `0` bits by scanning the associated pixels. The selecteddata transmission lines that represent `1` bits are leftnon-illuminated. The middle eight lines 30(2)-30(9) represent one byteof programming information being optically transmitted to watch 12. Topline 30(1) represents a start bit and bottom line 30(10) represents astop bit that are used for timing and error detection. Because of thescanning nature of the cathode ray of CRT monitor 14, these patternsproduce a serial light emission from CRT monitor 14 which isrepresentative of a serial bit stream. Each display frame represents onebyte. A new line grouping is presented for each sequential display frameso that each such display frame represents a different data byte.

FIG. 4 shows an external face of the programmable watch 12, which isillustrated for discussion purposes as the Timex® Data-Link™ watch. Itis noted that other watch constructions as well as other portableinformation devices can be used in the context of this invention. Watch12 includes a small display 32 (such as an LCD), a mode select button34, a set/delete button 36, next/previous programming buttons 38 and 40,and a display light button 42. Optical sensor 13 is positioned adjacentto display 32. In the programming mode, display 32 indicates theprogramming option, and what data is being entered therein. During thenormal operational mode, display 32 shows time of day, day of week, orany other function common to watches.

Referring now to FIG. 5, light sensor 13 of watch 12 is coupled to adigital serial receiver or UART 60. UART 60 may be a conventional,off-the-shelf circuit which receives data in eight-bit words surroundedby start and stop bits. The UART decodes the optical patterns to extractthe data bits transmitted from the computer. Watch 12 includesconversion circuitry (not shown) to produce a level-based serial signalfrom the edge-based signal generated by computer 11 and CRT 14. The UARTis coupled to an internal bus 62, which is preferably an eight-bit bus.Inputs received from the control buttons on the watch, referencedgenerally by box 64, are detected and deciphered by button controlcircuit 66 and placed on bus 62. The watch also includes a CPU (CentralProcessing Unit) 68 for performing the data processing tasks, a ROM(Read Only Memory) 70 for storing initial power-up programs and otheridentification information, and a RAM (Random Access Memory) 72 for datastorage. ROM 70 has an example capacity of approximately 16 Kbytes,while RAM 72 has an example capacity of 1 Kbyte. A display RAM 74 isprovided to temporarily store data used by display driver 76 to depictvisual information on display 32. These components, including the UARTcircuit, are preferably incorporated into a single microprocessor-basedintegrated circuit. One appropriate microprocessor IC is available fromMotorola Corporation as model MC68HC05HG.

To program the watch, the computer is first loaded with a compatibletime management software and optical pattern generating software. Oneexample time management software is Microsoft's® Schedule+™ for Windows®and a suitable optical pattern generating software is Timex® Data-Link™communications software. The user selects a desired option from a menuof choices displayed on the monitor in a human-intelligible form. Forinstance, suppose the user wants to enter his/her appointments and tasksfor the month of January, including a reminder for his/her mother'sbirthday on Jan. 18, 1995. The user inputs the scheduling information onthe computer using a keyboard and/or mouse input device. The user thensets the watch to a programming mode using control buttons 34-40 andholds optical sensor 13 facing the monitor screen 22. A sequence ofchanging optical patterns having horizontal contiguously-scanned linesbegin to flash across the monitor screen as shown in FIG. 3 to opticallytransmit data regarding the various appointments and tasks. In about 20seconds, the system will have transmitted as many as 70 entries,including the birthday reminder.

Referring back to FIG. 3, note again that the spacing of the datatransmission raster lines relative to the overall total of raster linesestablishes the transmitted bit rate. For example, the Timex Data-Link™watch currently receives data at a bit rate of 2048 bits per second.Accordingly, the successive data transmission raster lines should occurat a temporal spacing of 1/2048 seconds or 488 microseconds. Assuming a60 Hz scan rate and 480 total data transmission and unused raster lines,individual raster lines of the display device are temporally spaced fromeach other by approximately ##EQU1##

(where the CRT's vertical retrace is assumed to occupy 10% of the totalframe refresh period). Accordingly, the data transmission raster linesrepresenting individual data bits should be spaced from each other by 13unused raster lines, to occur every 14 raster lines (488/35). Thisspacing will result in the data transmission raster lines occurringtemporally at a rate of 2048 times per second.

Unfortunately, this calculation is dependent upon the display device'sframe scan rate or period. As mentioned above, this may vary fromcomputer to computer. It would be desirable to measure the frame scanperiod at installation. Most graphic controllers have a vertical retraceregister which indicates that the associated CRT is performing avertical refresh. Theoretically, this register could be monitored andthe time between vertical retraces measured to determine the timeconsumed for each CRT display frame. In practice, however, it isdifficult to make this measurement with accuracy within the programmingconstraints of a conventional personal computer.

FIG. 6, however, illustrates a method of calibrating the spacing of datatransmission raster lines of a CRT such as that described above toestablish a desired serial transmission bit rate. CPU 15 and programmeddata processor 17 form the means for performing the steps shown. A firststep 102 comprises setting internal timer 24 to generate timing signalsat a predetermined frequency. This frequency is preferably significantlygreater than the frame scan frequency to be measured. In preferredimplementations, the timing signal frequency is at least 10 timesgreater than the frame scan frequency or at least 1000 cycles persecond, with a frequency of 1000 cycles per second being most preferred.

A subsequent step 104 comprises counting a predetermined number of framescans, defining a selected measurement period. The predetermined numberof frame scans is preferably equal to at least 250. The preferredembodiment counts 500 frame scans. Step 104 is accomplished bymonitoring the vertical refresh register associated with CRT 14 andcounting the number of vertical refreshes. This number corresponds tothe number of frame scans of CRT 14.

A step 106 comprises counting the number of timing signals from timer 24which occur while counting the predetermined number of frame scans.Timing cycles could alternatively be counted in response to interruptsgenerated by internal timer 24.

Decision block 107 indicates that steps 104 and 106 are repeated untilthe predetermined number of frame signals has been counted. Note thatsimilar results could be obtained by counting the number of frame scansoccurring during a predetermined number of timing signals.

The steps described above allow a subsequent step 108 of deriving aframe scan period. This calculation is based upon the predeterminedfrequency of the timing signals, the predetermined number of framescans, and the number of timing signals counted while counting thepredetermined number of frame scans. More specifically, this calculationis performed by dividing the predetermined number of frame scans countedby the predetermined frequency of the timing signals and the number oftiming signals counted as follows: ##EQU2##

where Pf is the frame scan period, framescans is the predeterminednumber of frame scans, freq is the predetermined frequency of the timingsignals, and number is the number of timing signals counted during thepredetermined number of frame scans.

For example, assume that the timer has been set to generate timingsignals at 1000 cycles per second, that these timing signal are to becounted for 500 frame scans, and that 7143 timing signals are detectedduring these 500 frame scans (flamescans=500, freq=1000, andnumber=7143). Using the above equation, ##EQU3##

or 70 cycles/second.

A step 109 comprises adjusting the derived frame scan period by apredetermined factor to account for the vertical retrace period of CRT14. The resulting number represents the actual time the CRT spends intracing its raster lines. It has been found that most CRT's useapproximately 10% of their total frame scan period in moving theelectron beam from the bottom to the top of the screen between scans ofthe screen. Accordingly, in the preferred embodiment the predeterminedfactor is equal to approximately 90% of the derived frame scan period:Pa=Pf×0.90=0.0128574 seconds, where Pa is the adjusted frame scanperiod.

A further step 110 comprises deriving the display device raster lineperiod based upon the derived frame scan period. This is done bydividing the adjusted frame scan period by the total number of availableraster lines per display frame: ##EQU4##

where Pr is the raster line period, Pa is the adjusted frame scan period(0.0128674 seconds), and lines is the total number of available lines(assumed in this case to equal 480).

Step 112 includes spacing the data transmission raster lines relative toeach other within the total number of available raster lines inrelationship to the derived frame scan period. If a bit rate of 2048bits per second is to be achieved, the data transmission raster linesmust be temporally spaced at intervals of approximately 488microseconds. In practice, the data transmission lines are spaced inaccordance with the following equation: ##EQU5##

wherein bitnumber is an integer indicating the relative position of thebit in a display frame and rasterline is the number of the raster line(from among all available raster lines numbered consecutively from topto bottom) at which the bit should be displayed. Using the examplenumbers discussed above, the first bit in a display frame would bepositioned at the 18th raster line: ##EQU6##

The second bit in a display frame would be positioned at the 36th rasterline: ##EQU7##

This spacing establishes the desired serial transmission rate to watch12.

It should be noted that not all of the above calculations need beexplicitly implemented. Rather, the steps in determining the correctspacing of data transmission raster lines may be integrated in a singlecalculation in which the above steps are only implicitly carried out.Specifically, while a step of calculating or deriving a frame scanperiod is explicitly recited herein, this and other individualmathematical steps may be implicit, rather than explicit, in thecalculations carried out by computer 11. Furthermore, the preferredimplementation of the invention implements calculations using integermath rather than the floating point math used above. When using integermath, it may be more convenient to make calculations in terms offrequencies then in terms of periods as in the discussion above.

The steps above allow an application program which is to transfer datavia selected data transmission raster lines of a CRT to automaticallydetermine the frame scan rate or period of the CRT and to therefore setthe correct temporal spacing of the data transmission raster lines toestablish a desired bit transmission rate. This can be done without userinvolvement and thus is a great improvement over previous methods ofcalibrating bit transmission rates.

In compliance with the statute, the invention has been described inlanguage more or less specific as to structural and methodical features.It is to be understood, however, that the invention is not limited tothe specific features described, since the means herein disclosedcomprise preferred forms of putting the invention into effect. Theinvention is, therefore, claimed in any of its forms or modificationswithin the proper scope of the appended claims appropriately interpretedin accordance with the doctrine of equivalents.

We claim:
 1. In a computer system which uses selected data transmissionraster lines of a frame-scanning display device for serial bittransmission to an external receiving device, wherein the datatransmission raster lines are selected from a total number of availableraster lines per display frame, a method of calibrating the spacing ofthe data transmission raster lines relative to each other within thetotal number of available raster lines to establish a desired serialtransmission bit rate, the method comprising the following steps:settingan internal timer of the computer system to generate timing signals at apredetermined frequency; counting the number of the timing signals whichoccur during a selected measurement period; counting the number of framescans of frame-scanning display device which occur during the selectedmeasurement period; spacing the data transmission raster lines relativeto each other within the total number of available raster lines inrelationship to the counted number of timing signals and the countednumber of frame scans, said spacing establishing the desired serialtransmission rate to the external receiving device.
 2. A method asrecited in claim 1 wherein the frame-scanning display device has a framescan frequency, the setting step further comprising setting the internaltimer to generate the timing signals at a frequency that issignificantly greater than the frame scan frequency.
 3. A method asrecited in claim 1 wherein the frame-scanning display device has a framescan frequency, the frequency of the timing signals being at least tentimes greater than the frame scan frequency.
 4. A method as recited inclaim 1 wherein:the selected measurement period is defined by theoccurrence of a predetermined number of frame scans; the predeterminednumber of frame scans is at least
 250. 5. A method as recited in claim 1wherein the selected measurement period is defined by the occurrence ofa predetermined number of frame scans.
 6. A method as recited in claim 1wherein the step of spacing the data transmission raster lines comprisesdividing the counted number of timing signals by the product of thecounted number of framescans and the frequency of the timing signals. 7.A method as recited in claim 1 and further comprising:deriving a framescan period of the frame-scanning display device based upon thepredetermined frequency of the timing signals, the counted number oftiming signals, and the counted number of frame scans; adjusting thederived frame scan period by a predetermined factor to account for avertical retrace period of the frame-scanning display device.
 8. In acomputer system which uses selected data transmission raster lines of aframe-scanning display device for serial bit transmission to an externalreceiving device, wherein the data transmission raster lines areselected from a total number of available raster lines per displayframe, a method of calibrating the spacing of the data transmissionraster lines relative each other within the total number of availableraster lines to establish a desired serial transmission bit rate, themethod comprising the following steps:setting an internal timer of thecomputer system to generate timing signals at a predetermined frequency;counting the number of the timing signals which occur during a selectedmeasurement period; counting the number of frame scans of theframe-scanning display device which occur during the selectedmeasurement period; deriving a frame scan period of the frame-scanningdisplay device based upon the predetermined frequency of the timingsignals, the counted number of timing signals, and the counted number offrame scans; deriving a raster line period by dividing the derived framescan period by the total number of available raster lines per displayframe; and spacing the data transmission raster lines relative to eachother within the total number of available raster lines in relationshipto the raster line period, said spacing establishing the desired serialtransmission rate to the external receiving device.
 9. A method asrecited in claim 8 and further comprising adjusting the derived framescan period by a predetermined factor to account for a vertical retraceperiod of the frame-scanning display device.
 10. A method as recited inclaim 8 and further comprising adjusting the derived frame scan periodby a predetermined factor to account for a vertical retrace period ofthe frame-scanning display device, wherein the predetermined factor isequal to approximately 10% of the derived frame scan period.
 11. Amethod as recited in claim 8 wherein the predetermined frequency is atleast 1000 timing signals per second.
 12. A method as recited in claim 8wherein selected measurement period is defined by the occurrence of apredetermined number of frame scans, the predetermined number of framescans being equal to at least
 500. 13. A method as recited in claim 8wherein the step of counting the number of frame scans includesmonitoring a vertical refresh register associated with theframe-scanning display device.
 14. A computer system which uses selecteddata transmission raster lines of a frame-scanning display device forserial bit transmission to an external receiving device, the computersystem comprising:a data processor; a frame-scanning display devicehaving a total number of available raster lines per display frame; aninternal timer which is set to generate timing signals at apredetermined frequency; the data processor being programmed to countthe number of timing signals and the number of frame scans of theframe-scanning display device which occur during a selected measurementperiod; the data processor being further programmed to space the datatransmission raster lines relative to each other within the total numberof available raster lines as they appear on the frame-scanning displaydevice based upon the predetermined frequency of the timing signals, thecounted number of timing signals, and the counted number of frame scans,said spacing establishing a desired serial transmission bit rate to theexternal receiving device.
 15. A computer system as recited in claim 14wherein the frame-scanning display device has a frame scan frequency,the frequency of the timing signals being significantly greater than theframe scan frequency.
 16. A computer system as recited in claim 14wherein the frame-scanning display device has a frame scan frequency,the frequency of the timing signals being at least ten times greaterthan the frame scan frequency.
 17. A computer system as recited in claim14 wherein the selected measurement period is defined by the occurrenceof a predetermined number of frame scans, the predetermined number offrame scans being equal to at least
 250. 18. A computer system asrecited in claim 14 wherein the data processor calculates a frame scanperiod by dividing the counted number of timing signals by a product ofthe predetermined frequency of the timing signals and the counted numberof frame scans.
 19. A computer system as recited in claim 14 wherein:thedata processor calculates a frame scan period by dividing the countednumber of timing signals by a product of the predetermined frequency ofthe timing signals and the counted number of frame scans; the dataprocessor determines spacing of the data transmission raster lines bydividing the frame scan period by the total number of available rasterlines per display frame to determine a raster line period.
 20. Acomputer system as recited in claim 14 wherein:the data processorderives a frame scan period by dividing the counted number of timingsignals by a product of the predetermined frequency of the timingsignals and the counted number of frame scans; the data processor isfurther programmed to adjust the derived frame scan period by apredetermined factor to account for a vertical retrace period of theframe-scanning display device.
 21. A computer system as recited in claim14 wherein the data processor counts the number of frame scans bymonitoring a vertical refresh register associated with theframe-scanning display device.
 22. A computer system which uses selecteddata transmission raster lines of a frame-scanning display device forserial bit transmission to an external receiving device, the computersystem comprising:a data processor; a frame-scanning display devicehaving a total number of available raster lines per display frame; aninternal timer which is set to generate timing signals at apredetermined frequency; the data processor being programmed to countthe number of timing signals and the number of frame scans of theframe-scanning display device which occur during a selected measurementperiod; the data processor being further programmed to derive a framescan period of the frame-scanning display device by dividing the countednumber of timing signals by a product of the predetermined frequency ofthe timing signals and the counted number of frame scans; the dataprocessor being further programmed to derive a raster line period bydividing the derived frame scan period by the total number of availableraster lines per display frame; the data processor being furtherprogrammed to space the data transmission raster lines relative to eachother within the total number of available raster lines as they appearon the frame-scanning display device in relationship to the derivedframe scan period, said spacing establishing a desired serialtransmission bit rate to the external receiving device.
 23. A computersystem as recited in claim 22 wherein the data processor is furtherprogrammed to adjust the derived frame scan period by a predeterminedfactor to account for a vertical retrace period of the frame-scanningdisplay device.
 24. A computer system as recited in claim 22 wherein thedata processor is further programmed to adjust the derived frame scanperiod by a predetermined factor to account for a vertical retraceperiod of the frame-scanning display device, wherein the predeterminedfactor is equal to approximately 10% of the derived frame scan period.25. A computer system as recited in claim 22 wherein the predeterminedfrequency is at least 1000 timing signals per second.
 26. A computersystem as recited in claim 22 wherein the selected measurement period isdefined by the occurrence of a predetermined number of frame scans, thepredetermined number of frame scans being equal to at least
 500. 27. Acomputer system as recited in claim 22 wherein the computer systemfurther comprises a vertical refresh register associated with theframe-scanning display device, the data processor being programmed tocount frame scans by monitoring the vertical refresh register.